Why does my iPhone search continually?

Iphone 5 cannot link to cellular service. wifi antenna working ...email works. Sim card exchanged and reset tried. Battery is good.
Does this need a new cellular antenna? New power strip for the antenna? New charging jack assembly?
Thanks
JB

This may be an issue that you have to take to the Apple Store. Have you tried backing up and restoring your phone? Or restoring your phone to factory settings? Are you updated to the latest release of iOS?